1.1 INTRODUCTION:

The human ear can hear the sound waves between 20 Hz to 20 kHz. This frequency range is known as “Audio Frequency Range”. The sound waves having frequencies above this audible range is known as “Ultrasonic Waves” or “Supersonic Waves”. Supersonic waves have the velocities higher than the velocity of sound i.e. more than 1200 km / hour. Ultrasonic waves can not be heard by a human being but a cat or dog may hear them. The wavelengths of ultrasonic waves are very small as compared to audible sound. The sound waves which have frequencies less than 20 Hz range are called “Infrasonic waves”

1.2 Production of Ultrasonic Wave:

The generator of ultrasonic wave is nothing but an oscillator, which can generate …show more content…

The high frequency A.C. voltage obtained from the Hartley oscillator circuit is applied to the crystal. The Hartley oscillator circuit consists of a tank circuit made up of parallel combination of inductance L1 & variable condenser C1. One end of the tuned circuit is connected to the plate of the triode valve V & while the other end connected to the grid. The coil L1 is tapped near the centre & joined to cathode. The quartz crystal ‘Q’ is connected parallel with variable condenser C1 & proper grid bias is obtained by means of grid leak register Rg. & grid condenser Cg.

The D.C. voltage is applied to the plate through Radio frequency choke (RFC). The radio frequency choke prevents the radio frequency current to pass through high tension battery. The condenser ‘Cb’ is a blocking capacitor which prevents the direct current to pass through the tank circuit & it by passes the radio frequency currents. The capacity of the variable condenser C1 is adjusted in such a way that the frequency of the oscillating circuit is tuned to the natural frequency of the crystal. Now crystal set into the mechanical vibrations & the ultrasonic waves are produced. The ultrasonic waves up to a frequency of 500 kHz with a moderate size quartz crystal can be produced by this method.

1.3 Applications of Ultrasonic Wave

1.3.1 Determination of the depth in a sea:

SONAR : (Sound Navigation &